[Intl_DxMedPhys] Gafchromic film

[Bob Kobistek]

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Yep, but for stuff like measuring CT beam collimation it doesn't matter. Crank up the mAs to get a good image, then take an image at half the mAs to use as a reference for FWHM. Sensitivity and fog level shouldn't matter


Robert J. Kobistek, MS, FACR, DABR, MRSE(MRSC™)
Medical Physicist
RJK Medical Physics, Inc.
440-463-7879

-----Original Message-----
From: Douglas Pfeiffer <xraydoug at me.com> 
Sent: Wednesday, June 3, 2026 11:06 AM
To: Nicole Ranger <nicoletranger at yahoo.com>
Cc: Bob Kobistek <bob at rjkmedphys.com>; DxMedPhys List <intl_dxmedphys_wd_osu_list at lists.osu.edu>
Subject: Re: [Intl_DxMedPhys] Gafchromic film

Yup. It just loses sensitivity, in my experience.


Doug
-------------
Sent from my iPhone - please excuse any typos that slip through!

> On Jun 3, 2026, at 9:01 AM, Nicole Ranger via Intl_dxmedphys_wd_osu_list <intl_dxmedphys_wd_osu_list at lists.osu.edu> wrote:
> 
> Thanks Bob.  I used large sheets in the past to assess skin dose distributions in fluoro procedures and the results were informative but baselines mattered there.  Glad to know the consensus is that they can be used almost indefinitely for QC.
> 
> Nicole
> 
> 
> Sent from my iPhone
> 
>> On Jun 3, 2026, at 11:55 AM, Bob Kobistek <bob at rjkmedphys.com> wrote:
>> 
>> I'd say as long as you can see a useable image, keep using the film. I left some sheets in my hot car over last summer. The sheets are much darker than new sheets, but I'm still using them for CT collimation testing. I can even scan and locate the FWHM with no problems.
>> 
>> 
>> Robert J. Kobistek, MS, FACR, DABR, MRSE(MRSC™) Medical Physicist RJK 
>> Medical Physics, Inc.
>> 440-463-7879
>> 
>> -----Original Message-----
>> From: Intl_dxmedphys_wd_osu_list 
>> <intl_dxmedphys_wd_osu_list-bounces+bob=rjkmedphys.com at lists.osu.edu> 
>> On Behalf Of Nicole Ranger via Intl_dxmedphys_wd_osu_list
>> Sent: Wednesday, June 3, 2026 9:33 AM
>> To: DxMedPhys List <intl_dxmedphys_wd_osu_list at lists.osu.edu>
>> Subject: [Intl_DxMedPhys] Gafchromic film
>> 
>> Good morning list,
>> 
>> I’ve used Gafchromic film extensively in the past in a dosimetry context where cumulative exposure during storage was important but for the Gafchromic that you use for imaging QC purposes (CT, Mammo, etc…) where the baseline exposure is less important so long as there is adequate contrast, what would you consider to be a useful timeframe before the film is less useful?  Just wondering if there is any downside when buying a box. We have relatively fewer devices here than I have had to support in the past so I’m not sure how quickly I will go through this stuff.
>> 
>> TIA
>> Nicole
>> 
>> 
>> Sent from my iPhone
>